Dynamoelectric machine rotor



July 19, 1966 REDIGER ETAL 3,262,000

DYNAMOELECTRIC MACHINE ROTOR Original Fil ed May 14, 1962 2 Sheets-Sheet 1 July 19, 1966 REDIGER ETAL 3,262,000

DYNAMOELECTRI C MACHINE ROTOR Original Filed May 14, 1962 2 Sheets-Sheet 2 United States Patent 3,262,000 DYNAMOELECTRIC MACHINE ROTOR Alvin L. Rediger, Zeeland, and Julius Slager, Holland,

Mich., assignors to General Electric Company, a corporation of New York Original application May 14, 1962, Ser. No. 194,540.

Divided and this application Sept. 16, 1965, Ser.

4 Claims. (Cl. 310-261) This is a division of our co-pe-nding application Serial No. 194,540 filed May 14, 1962.

This invention generally relates to the manufacture of dynamoelectric machines and more particularly to an improved method of fabricating laminated rotors having cast squirrel-cage winding construction.

In the mass production of laminated rotors incorporating cast squirrel-cage windings, that is, conductor bars integrally joined at each end of a laminated stack by end rings, there has been a practical difficulty in providing accurately skewed conductor slots while maintaining economy in the fabrication of the rotors; i.e., relatively low equipment and process costs. In one approach, punched out laminations, formed with vent holes or ducts between the rotor bore and the slots, are initially stacked such that a number of spiraling pins enter the vent holes to skew the slots. The stacked laminations are then compressed by elaborate equipment and while held under compression, the squirrel-cage winding is cast on the stack by a pressure or centrifugal casting technique. Not only is the procedure costly due to the type of equipment and labor involved, but in addition where no vent holes exist in the laminations, it is impossible to follow this procedure to obtain an accurate skew of the slots.

With specific reference to the manufacture of rotors having counterbores and balance weights attached on studs made integral with end rings to compensate for an unbalance in the mass system with which the rotor is associated; e.-g., a single piston compressor with a crank-shaft introducing a dynamic unbalance into the system, difficulty has also been experienced in satisfactorily securing the laminations together, especially in the region of the counterbore where the bore of the lamin'ations is in spaced relation to the stationary rotor supporting structure. Furthermore, when the balance weight mounting studs are integrally provided with one end ring, there is a tendency for the studs and winding to be cast with a non-uniform density as a result of (at least in part) voids contained in the hardened casting, which in turn adversely affect the conductivity of the winding and the dynamic balance of the rotor, both conditions being detrimental to the performance of the rotor.

' Accordingly, it is a general object of the present invention to provide an improved laminated rotor capable of being mass produced by simple and low cost manufacturing procedures utilizing inexpensive equipment.

It is a more specific object of the invention to provide an improved structurally strong, yet economical laminated rotor fabricated with cast windings of generally uniform density which have casting sprues recessed below the outer surface of the rotor winding.

In carrying out the objects of the present invention, we provide an improved rotor fo ruse in an induction type dynamoelectric machine in which the rotor is fabricated with a laminated magnetic core carrying a squirrelcage secondary winding cast from non-magnetic material such as aluminum. The rotor core has a central bore, counterbored at one end to enlarge the bore at that location, and at least two spaced apart shallow, slightly penetrating welds extending substantially the axial length of the core applied before the winding was formed in the core, the weld if located on the outer surface of the core being partially removed after the winding has been cast without introducing dynamic unbalance. At one end of the rotor the winding includes a number of angularly spaced recesses having non-machined sprues therein provided below the surface of the winding and a balance weight mounted over one or more of the recesses by supporting studs.

With this construction, the remaining portions of the welds and cast win-ding firmly secure the laminations together especially in the inherently weak region of the core at the counterbore where such securement is quite advantageous. Further, the rotor construction does not introduce dynamic unbalance by virtue of the rotor components mentioned above and the cast winding is generally of uniform density in spite of the economics permitted in its manufacture; e.g., the non-machined sprues which do not interfere with the mounting of the balance weight yet require no machining operation.

The subject matter which we regard as our invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. Our invention, itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings which illustrate the preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a fragmentary top view of loosely arranged stamped out rotor laminations in stacked relation;

FIGURE 2 is a side elevational view, partly broken away, illustrating the application of a weld on the periphery of the lam-inations of FIGURE 1 when the conductor slots are disposed is skewed axial register and the stack is held under compression;

FIGURE 3 is a partial side elevational view, broken away in parts, of the welded stack of laminations in position preparatory to the casting operation for forming the stack with a cast squirrel-cage winding;

FIGURE 4 is a view similar to that of FIGURE 3 illustrating the casting operation;

FIGURE 5 is an enlarged fragmentary view in section of a portion of the die and sprue port structure of the equipment shown in FIGURES 3 and 4;

FIGURE 6 is a fragmentary sectional view through the rotor, illustrating the step of finishing the periphery of the rotor into a smooth accurate dimension while simultaneously removing at least a portion of the welds;

FIGURE 7 is a view in perspective, partially broken away to illustrate structural details, of the finished rotor fabricated in accordance with the preferred embodiment of the invention; and

FIGURE 8 is an enlarged fragmentary side view in section of a part of the rotor of FIGURE 7 to show details.

Referring now to the drawings in more detail, for purposes of explanation, the preferred embodiment of the invention has been applied in connection with an induction rotor 10 (FIGURE 7), suitable for use in a motorcompressor unit to drive a single piston compressor (not shown) in which the compressor crankshaft introduces a dynamic unbalance into the mass system with which the rotor is associated. An example of this type of unit is illustrated in the US. Patent No. 3,157,806, granted on November 17, 1964 to W. R. Hoffmeyer and J. H. Johnson, and assigned to the same assignee as the present application.

In the present exemplification, FIGURES 1-6 inclusive disclose the preferred fabricating procedure for producing a rotor constructed in accordance with our invention. More specifically, as shown in FIGURES 1 and 2, we

initially assemble a predetermined number of disc shaped laminations 11 and 12, conventionally stamped out of magnetizable sheet iron or steel material. To illustrate the inventon, laminations 11 and 12 include central holes 13 and 14 respectively, and a plurality of angularly spaced apart closed conductor slots 15 disposed radially beyond the central holes and adjacent periphery 16 of laminations, which is somewhat rough from the tearing action in the punch operation. In order to achieve a skew of the conductor slots and the proper alignment of the central holes, the laminations may be loosely arranged in a stack 17 on a suitable fixture (see FIGURE 2), in which a base 21 is provided with three angularly spaced apart (e.g., approximately 120) upright rods or pins 22 for receiving slots 15 and spiralling them at the proper angle to form skewed conductor passageways extending entirely through the stack. Central holes 13 are aligned to furnish a bore adapted to have an interference fit with a rotatable shaft (not seen) and enlarged holes 14 of laminations 12 provide a counterbore for accommodating a part of the stationary rotor supporting structure of the motor-compressor unit (not shown) in spaced relation.

After the laminations have been arranged on the fixture as previously described, they are then compressed axially with approximately the same force as that required for the subsequent casting operation. Generally speaking, the necessary minimum force is in the neighborhood of 100 pounds per square inch of gross punching area. While stack 17 is held in axial compression, several welds are applied in a predetermined fashion (to be explained hereinafter) on peripheral surface 16 to secure the laminations firmly together in the desired relation for subsequent fabrication steps. FIGURE 2 shows one inexpensive yet satisfactory manner in which the foregoing may be readily accomplished. The equipment includes a rotatable turntable 24 on which base 21 is fixedly attached and a revolvable piston assembly 25, having apertures 26 to complement the ends of skewing rods 22, and capable of regulated compressive movement toward and away from turntable 24.

It should be noted at this time that we prefer to fuse the skewed or spiraled stack of laminations together by at least two, preferably three but not substantially more, light or shallow welding beads 27, provided in generally equally spaced apart angular relation on the peripheral surface 16 of stack 17. These beads preferably extend the longitudinal length of the stack on the solid portion thereof, intermediate and parallel to a pair of adjacent conductor passageways defined by slots 15. Preferably the depth of weld penetration into the stack is shallow in extent; that is, the penetration should be such that during the turning down step in which the peripheral surface of the stack is finished into an accurately dimensioned cylindrical surface (FIGURE 6), a greater portion, if not all, of the welding bead itself may be readily removed. As an example, for a nominal three inch diameter stack, the penetration should not be substantially in excess of inch beyond the finished peripheral surface of the stack. In this way, the possibility of introducing undesirable and uncontrollable dynamic unbalance and rotor noise are essentially prevented.

In actual practice, satisfactory results have been obtained with the use of a commercially available are welding machine employing inert tungsten, with the welding head 28 suitably mounted to move parallel to the skew of the laminations. The welding machine, one of straight polarity, had the following characteristics: welding current-450 to 160 amps; welding voltage volts; weld speed-40 to 50 inches/minute; electrode diameter- X inch; and pure argon shielding gas flowing between to cubic feet per hour. For indexing turntable 24 to lock the stack in the proper location relative to welding head 28, a common plunger assembly 29 may be utilized. Once the welding operation has been completed, piston is t raised and the stack of laminations removed from fixture 20.

The welded together stack may be annealed in the conventional way for stress relieving purposes and either stored for subsequent use or conveniently transported by conveyor (not shown) to the casting operation. It will be appreciated that. among other things to be explained hereinafter, welds 27 function as a temporary holding fixture for maintaining the stack of laminations under compression both prior to and during the casting process, now to be described in connection with a pressure type aluminum casting procedure shown in FIGURES 3 and 4.

Turning now to the illustrated pressure type casting apparatus employed in the casting operation, it comprises a casting chamber 30 and a pressure ram head 31 positioned directly above the chamber and capable of being reciprocated relative to the chamber by any suitable means, as by a hydraulic driving piston. Chamber 30 is formed in halves which are hinged at 34 upon a trunnion shaft 35 mounted in a suitable base 36. The two halves are normally held together by a detachable connection or latch 37. A heated pot 32 containing a supply of molten casting material 33, e.g., aluminum, is located on base 36 next to chamber 31 for conveniently transmitting the correct amount of molten material by a ladle or the like to chamber 30 at the start of each casting cycle.

The casting dies for forming the squirrel-cage winding include an upper die plate 40 (as viewed in the drawings), adapted to be removably positioned at one side face of stack 17, and a lower die plate 41 for mounting at the other side of the stack, adjacent the counterbore of the rotor in the exemplification. The plates are maintained in tight engaging relation at the stack side faces for the casting process by a rod 42 (FIGURE 3), fastened at one end to the center of lower plate 41 and extending up through the bore of the stack. The other end of the rod passes through plate 40 and is locked thereto by the threaded interengagement between externally threaded rod end 43 of the upper end of rod and a nut 44 partially received in plate depression 45. Through the threaded engagement of an internally threaded hole 46 formed in ram head 31 and the externally threaded rod end 43, the laminated stack and the attached die plates may move as a unit with the ram head.

With reference to the preferred casting die forms, plates 40 and 41 respectively include generally annular end ring forming cavities 52 and 51 respectively each having a somewhat U-shaped molding wall in communication with the ends of the skewed conductor passageways defined by slots 15 for admission of molten metal, denoted by number 53 in FIGURE 3. Lower die plate 41 is provided with a pair of spaced apart elongated slightly tapering downwardly extending weight supporting stud cavities 54 and 55. As shown in FIGURE 3, the casting entrances of the stud cavities are contained on the bottom wall (as viewed in the drawing) of cavity 51. A plurality of spruing ports 57 for the introduction preferably of metal 53 from chamber 30' to the cavity 51, frusto-conical in configuration and corresponding in number to the number of conductor passageways incorporated in the rotor, are disposed around the bottom wall of cavity 51, several of the ports being included between stud cavities 54 and 55. An insert or sleeve 58 is positioned in each port such that its egress 59 projects a short predetermined distance into cavity 51. The taper of the ports and inserts is in the neighborhood of 5, with the insert egress having the minimum cross section area for locking and fluid guiding purposes.

For best casting results, the egress cross-section area for the individual inserts should be substantially in the range of 0.0069 to 0.0145 square inch, and the ratio of the weight of the casting material in pounds relative to the total egress area in inches should be below seven. As will become more apparent hereinafter, the casting arrangement just described eliminates the necessity of machining off sprues normally formed during the casting process while permitting the easy and inexpensive replacement of parts, such as inserts 58, after long continued use. Further, during the casting operation, the foregoing minimizes the possibility of cold flow of the casting material and other undesirable causes of voids, to assure a filling of the cavities and a winding and supporting studs of enhanced uniform density.

Referring now in particular to the casting procedure, operation is initiated with the component parts in the position shown in FIGURE 3, that is, with the assembled die, stack, and ram head unit raised above chamber 30 which has the requisite amount of molten aluminum. Head 31 is lowered at a speed of 65-75 feet per second until lower die plate 41 enters the confines of chamber 30. Continued downward movement of the plate 41 causes the molten aluminum to be forced upwardly with a preselected pressure through inserts 58, first into cavities 51, 54 and 55, then through the slot passageways into upper cavity 52, filling all casting spaces in the stack and plates. Trapped gases in the dies may be exhausted to the atmosphere through vents in die 40 which are sufficiently small to prevent the escape of molten metal from the casting cavities.

Since stack 17 and the die plate are at a lower temperature than the molten aluminum, they absorb heat from the aluminum, hardening it. It will be observed from FIGURE 4 that the hardened aluminum in the dies and stack 17 provide conductor bars 61 in the slot passageways, integrally joined at each end by annular end rings 62 and 63, to form the squirrel-cage windings, as Well as studs 64 and 65 for supporting balance weights 66 (FIG- URE 7). In addition, as seen in FIGURES 4 and 5, with the egresses 59 of the frusto-oonical shaped port inserts 58 extending upwardly into bottom cavity 51, a conical sprue 67 is produced within egress 59 which mates in a point contact with hardened upstanding runners 68 of an excess metal slug 69. Upon upward movement of ram head 31 once again to the raised position of FIGURE 3, sprues 67 and runners 68 shear at a point beneath the outer surface 70 (FIGURE 5). Consequently, egresses 59 furnish tapered recesses 71 in end ring 63 surrounding sprues 67 which do not have to be removed by a subsequent machining step. Hardened slug 69 may thereafter be returned to heated pot 32 to be liquefied for reuse.

Upon completion of the casting procedure, die plates 40, 41 and stack 17 are dismantled from ram head 31 and the laminated stack is disassembled from between the plates. Thereafter stack 17 is transferred to the final turning operation, illustrated by FIGURE 6, Where the outer periphery of the stack is turned down to an accurate diameter by any suitable means, such as cutting tool 73, to produce an accurately dimensioned smooth finished rotor surface 16a, Coincident with this surface finishing step, a major portion, but not necessarily all, of each weld 27 is removed. Either before this finishing step is performed or after it has been accomplished, balance weights 66 (one being shown in FIGURES 7 and 8) can be secured in place on studs 64 and 65 by a simple staking procedure.

The completed rotor 10, formed in accordance with the preferred embodiment of our invention, is shown in FIG- URES 7 and -8, revealing certain advantageous features of the invention, especially significant when the rotor is of the type having balance weights and a counterbore at one end for accommodating a part of the rotor supporting structure. An improved cast winding and studs of enhanced uniform density are provided, and in spite of the fact that casting sprues 67 have not been removed by a machining operation, balance weights may be attached in close proximity to outer surface 70 of the end ring 63 without interference in the mounting by the sprues. Moreover, rotor 10 may include accurately skewed conductors whether or not the rotor incorporates vent holes or ducts. In addition, if desired, not all of welds 27 need be removed to aid the lamination securing action of the cast winding thereby augmenting the structural strength of the rotor. This is especially critical when the rotor includes a counterbore and runs at elevated temperatures at which the winding expands, resulting in the loss of friction between the laminations. Furthermore, the remaining portion of the welds will not adversely affect the dynamic balance and noise characteristics of the rotor.

It should be apparent to those skilled in the art, while we have shown and described what at present is considered to be the preferred embodiment of our invention in accordance with the patent statutes, changes may be made in the structure disclosed without actually departing from the true spirit and scope of this invention, and we therefore intend to cover in the following claims all such equivalent variations as fall within the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A rotor for use in an induction type dynamoelectric machine comprising a stack of laminations having a central bore counterbored at one end for receiving rotor supporting means, a plurality of conductor slots disposed radially beyond said bore in skewed axial register through the stack, conductors of nonmagnetic electrically conducting material cast in said slots and interconnected at each end of the stack by end rings to form a cast squirrel-cage winding, spaced apart mounting studs integrally provided on at least one of said end rings, and a plurality of angularly spaced apart recesses surround casting sprues disposed angularly around the end ring, at least one of said recessed sprues being positioned between the studs, balance weight means secured to said mounting studs adjacent an end ring without interference from said sprues, more than one angularly spaced apart shallow weld formed along a periphery of the stack at least in the region of the counterbored portion thereof prior to the casting of the conductors whereby said welds and winding conjoint-1y hold said laminations together in the counterbored region of the stack.

2. A rotor for use in an induction type dynamoelectric machine comprising a stack of laminations having a finished smooth peripheral surface and a plurality of conductor slots in axial register through the stack, conductors of nonmagnetic electrically conducting material cast in said slots and interconnected at each end of the stack by annular end rings to form a cast squirrelcage winding, at least two angularly spaced apart shallow continuous Welds formed along a substantial axial peripheral length of said stack, the welds being applied prior to the casting operation for holding the stack together and partially removed during the finishing of said peripheral surface, the winding and remaining welds conjointly securing said stack together Without introducing dynamic unbalances.

3. A rotor for use in an induction type dynamo electric machine comprising a stack of laminations having a finished smooth peripheral surface and a plurality of conductor slots in axial register through the stack; conductors of nonmagnetic electrically conducting material cast in said slots and interconnected at each end of the stack by annular end rings to form a cast squirrelcage winding; one end ring having mounting stud means and a plurality of angularly spaced apart recesses surrounding non-machined casting sprues, with at least one of said recesses being positioned between said mounting stud means for supporting balance weight means thereon; and the non-machined casting sprue of said one recess being disposed beneath the outer surface of said one end ring, whereby mounting of the balance weight means on the mounting stud means will be free of interference from the one recess and its non-machined casting sprue; at least two angularly spaced apart shallow continuous Welds formed along a substantial axial length of said stack; the Welds being applied prior to the casting operation for holding the stack together and being partially removed during the finishing of said peripheral surface, the Winding and remaining welds conjointly securing said stack together Without introducing dynamic unbalances.

4. A rotor for use in an induction type dynamoelectric machine comprising a stack of laminations having a central bore; a plurality of conductor slots disposed radially beyond said bore in axial register through the stack; conductors of nonmagnetic electrically conducting material cast in said slots and interconnected at each end of the stack by end rings to form a cast squirrelcage winding; spaced apart mounting studs integrally provided on at least one of said end rings; a plurality of angularly spaced apart recesses surrounding casting sprues References Cited by the Examiner UNITED STATES PATENTS 2,316,635 4/1943 Staak 310-51 X 2,447,383 v8/1948 Wightman 3105l 2,528,154 10/1950 Ludwig et al 310-211 2,991,378 7/1961 Barney 3l0--211 3,154,705 10/1964 Essenburg 310-51 MILTON O. HIRSHFIELD, Primary Examiner.

L. L. SMITH, Assistant Examiner. 

1. A ROTOR FOR USE IN AN INDUCTION TYPE DYNAMOELECTRIC MACHINE COMPRISING A STACK OF LAMINATIONS HAVIN A CENTRAL BORE COUNTER-BORED AT ONE END FOR RECEIVING ROTOR SUPPORTING MEANS, A PLURALITY OF CONDUCTOR SLOTS DISPOSED RADIALLY BEYOND SAID BORE IN SKEWED AXIAL REGISTER THROUGH THE STACK, CONDUCTORS OF NONMAGNETIC ELECTRICALLY CONDUCTING MATERIAL CAST IN SAID SLOTS AND INTERCONNECTED AT EACH END OF THE STACK BY END RINGS TO FORM A CAST SQUIRREL-CAGE WINDING, SPACED APART MOUNTING STUDS INTEGRALLY PROVIDED ON AT LEAST ONE OF SAID END RINGS, AND A PLURALITY OF ANGULARLY SPACED APART RECESSES SURROUND CASTING SPRUES DISPOSED ANGULARLY AROUND THE END 